1. Field of the Invention
This invention relates to gas turbine engine rotor attachment and particularly to heat shields and axial retention for bolts used to connect turbine shafts.
2. Description of Related Art
Gas turbine engines conventionally transfer rotational mechanical energy from turbine sections of the engine to the fan and compressor sections via shaft assemblies that are bolted together for easy assembly and disassembly. Ease of assembly and disassembly provides many benefits from a cost standpoint and enhance modular designs which have been developed to help ship and install gas turbine engines. Examples of such modular engines are disclosed in U.S. Pat. No. 3,842,595 entitled "Modular Gas Turbine Engine" by Smith et al and in U.S. Pat. No. 3,823,553 entitled "Gas Turbine With Selfcontained Power Turbine Module" by Smith, both assigned to the same assignee as the present invention.
Due to the large size of modern high bypass ratio fanjet engines, and particularly their fan sections, it has become useful to incorporate modularity into engine designs. Modularity enhances the engine's assembly and disassembly and facilitates shipment of the engine and its part for original installation, overhaul, repairs, and retrofitting.
Bolt assemblies to secure shaft sections for the low pressure turbine are often not accessible from the low pressure turbine are often not accessible from the rear during assembly. Axial bolt retention means are required during assembly because such bolt heads lie in closed cavities. Heat shielding the bolts from the hot gases passing through rear stages of the low pressure turbine is also highly desirable if not often required to prolong the useful life of the assembly and increase engine reliability.
Prior engine designs such as the one illustrated in FIG. 1 have incorporated split ring retainers 2 disposed in circumferential grooves 4 formed in the shank 6 of and to retain the bolt 8 which is used to attach a forward rotor element 10 to an aft rotor element 12. Another prior art design is illustrated in FIG. 2, and uses an individual bolt hook 14 to retain the bolt 8 which attaches forward rotor element 10 to aft rotor element 12. Yet another apparatus shown in the prior art is a retention clip disclosed in U.S. Pat. No. 4,887,949 entitled "Bolt Retention Apparatus" by Dimmick, III et al. All of these designs add weight, increase the number of engine parts, and increase the complexity of the engine and assembly and disassembly procedures. Circumferential grooves reduce the shanks load carrying capability and split rings and clips are subject to and may also introduce undesirable engine vibrations.